Have a 96 buick park ave when I go over 40 she chugs and vibrates help

What is your question?

She has brand new tires and alignment, oil change, replaced plugs and wires, changed transmission fluid and filter along with fuel filter. If I stop accelerating it stops. It was worse but after the changes has lessened she also only does this when warm. She has over 170,000 miles as well. Any ideas would be greatly appreciated.

What makes this problem better or worse?

Worse when warm and over 40 if i take foot off gas it stops

How long has your 2003 Buick Century had this problem?

A few weeks